1. Field of the Invention
The present invention relates to a reactor with an electrical insulating film, fuel cell apparatus, electronic device and method of producing the electrical insulating film.
2. Description of the Related Art
A fuel cell is a reactor for generating electric power by an electrochemical reaction of hydrogen and oxygen. Research and development of fuel cells are being widely done as a main stream power source system of the next generation. Especially, solid oxide fuel cells (hereinafter referred to as SOFC), which have high power generation efficiency due to high temperature operation, are being developed.
The SOFC includes a power generating cell in which a fuel electrode is formed on one face of a solid oxide electrolyte and an oxygen electrode is formed on the other face.
The oxygen supplied to the oxygen electrode is ionized by the electron supplied from the oxygen electrode (O2−). The O2− permeates the solid oxide electrolyte from the oxygen electrode side to the fuel electrode side. The O2− oxidizes the fuel gas supplied to the fuel electrode and releases the electron of the fuel electrode. Here, the fuel gas is mainly hydrogen gas, and hydrogen gas and a by-product, carbon monoxide, from reforming fuel such as methanol in which the composition includes hydrogen atoms are used.
The electron from the anode output electrode connected to the fuel electrode passes through an outer circuit and returns to the oxygen electrode by a cathode output electrode connected to the oxygen electrode, and ionizes the oxygen in the oxygen electron. This is how the chemical energy of fuel gas and oxygen is converted to electric energy.
Since the power generating cell of the SOFC operates at a high temperature, a thin film heater including a conductor is provided with an electrical insulating film in between, and the thin film heater performs the heating.
Since the reforming reaction of the fuel gas is also performed at a high temperature, a thin film heater including a conductor is provided in the reformer and the thin film heater heats the reformer (see for example, Japanese Patent Application Laid-Open Publication No. 2004-256837). When the reformer is made from metal and the like, the thin film heater including the conductor is provided with an insulating film in between.
In order to suppress the loss of heat due to radiation from the thin film heater, an electrical insulating film is provided on the surface of the thin film heater and the surface of the thin film heater is covered with a radiation prevention film with an insulating film in between (see for example, Japanese Patent Application Laid-Open Publication No. 8-166269).
The insulating film is formed by, for example, applying SiO2 so as to fill in the unevenness of the thin film heater flatly on the surface of the thin film heater. The radiation prevention film is formed on the surface of the insulating film.
However, the SiO2 film formed with the applying method becomes an amorphous (non-crystalline) structure, and the linear expansion coefficient is 0.5-0.6 (×10−6/° C.). The linear expansion coefficient of the metal used in the power generating cell and the thin film heater of the SOFC is 10-14 (×10−6/° C.), and there is a big difference between the linear expansion coefficient of the power generating cell and the thin film heater and that of the insulating film. Thus, when the insulating film is provided by the applying method, the insulating film and the thin film heater with a large difference in linear expansion coefficients are in contact with each other, and when the temperature of the reactor becomes high, the insulating film may crack or peel off. This may reduce the reliability of the electrical insulation between the thin film heater and the radiation prevention film (including a conductor such as Au and the like).